Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

595
FXUS63 KLOT 092324
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
624 PM CDT Sat May 9 2026

.KEY MESSAGES...

- Warm, dry, and breezy conditions will lead to a continued
  elevated risk for brush fires across northern Illinois this
  afternoon.

- Cooler conditions are in store Sunday into Monday with
  showers and storm chances returning on Tuesday.

&&

.DISCUSSION...
Issued at 300 PM CDT Sat May 9 2026

Low pressure centered over Ontario is slowly progressing east
today with a trailing cold front extending southwest across the
lower Great Lakes, currently located near the Illinois and
Kankakee River valleys here locally. Deep mixing in the wake of
this boundary has allowed dewpoints to mix down quickly into the
lower 30s. In tandem, winds have increased this afternoon with
frequent gusts into the 25-35 mph range. Sporadically higher
gusts over 40 mph can`t be ruled out for the next few hours.
This paired with temperatures in the low to mid 70s have
resulted in relative humidity values dropping into the 20s.
While recent rains have allowed many areas to green up, an
elevated threat of fire spread will exist through the rest of
this afternoon. Also can`t rule out patches of blowing dust near
any recently worked over farm fields.

Ahead of the front an axis of marginal MLCAPE exists (~250-500
J/Kg). Some cumulus has started to bubble up south of the
Kankakee River early this afternoon with showers and isolated
storms having developed farther east across northern Indiana.
Can`t rule out a stray shower developing prior to sunset as the
cold front continues to progress south across the area. Think
that the notable dry air within the vicinity of the front should
hinder more robust shower development and hence keep the
thunder potential east of the area.

Winds will steadily ease with sunset with temperatures falling
into the low to mid 40s as skies clear out overnight. A separate
disturbance moving across southeast Nebraska may bring a narrow
axis of light showers across the far southern CWA and across
central IL overnight and have accordingly held onto low precip
chances (15-25%) south of a Pontiac to Rensselaer line.

Mother`s Day and Monday will feature cooler temperatures, with
highs in the 60s (50s near the lakeshore). While a closed mid-
level low continuing to linger across the Great Lakes region
could lead to spotty light showers/sprinkles development at
times within the vicinity of any vort lobes, dry conditions are
favored here locally given dry low-levels and overall weak
forcing mechanisms.

Attention then turns to Tuesday when a shortwave dives across
the area. A band of showers and thunderstorms may develop along
an associated cold front northwest of the area and then progress
southeast across the area. Ample shear will be in place amidst
strong northwest mid-upper jet and steady southwesterly low-
level flow. Marginal instability owing to poorer mid-upper lapse
rates may inhibit more robust thunderstorm
development/maintenance into the local area and accordingly the
severe weather threat. Still plenty of time to iron out the
details though. The strong southwesterly surface winds (gusts to
35-40+ mph) may also lead to some blowing dust concerns,
especially in rural and open areas near recently worked over
farm fields.

Beyond Tuesday, temperatures briefly cool down once more in the
wake of the cold front, with high temperatures on Wednesday
back in the 60s. We then warm up gradually each day through the
end of the week as upper level ridging builds across the central
CONUS into the Upper Midwest by the weekend with additional
shower/storm chances (20-30%) late Thursday into Friday.

Petr

&&

.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 624 PM CDT Sat May 9 2026

Aviation forecast concerns for the 00Z TAFs:

- Lake-assisted wind shift to northeast possible with boundary
  currently pushing south along the IL Lake Michigan shore. Low
  confidence just how far inland northeast winds will push
  against otherwise gusty NNW flow. Much higher confidence in a
  period of NNE flow at GYY this evening.

- Breezy NW winds develop again Sunday midday/afternoon, with
  gusts 20-25 kt.

Latest surface analysis depicts 997 mb low pressure tracking
north of Lake Huron early this evening, with a cold front
trailing through lower MI into IN and southeast IL. A secondary
cold front was pushing southeast across southern WI, with a
lake-enhanced portion pushing more quickly southward across Lake
Michigan. This boundary is easily noted in ORD TDWR imagery
pushing inland into eastern Lake and northeast Cook counties in
IL. This may bring a wind shift to NNE into ORD/MDW early this
evening, though confidence in it moving fully across both
airfields is somewhat low given gusty NNW flow across southern
WI/northern IL. Have elected to indicate a TEMPO for NE winds at
both ORD and MDW from 01Z, and if boundary pushes inland more
strongly may have to consider a several hour period of NE flow.
Wind gusts initially around 25 kt should gradually diminish
after sunset, with winds then favoring light North-northwest
overnight into Sunday morning. After sunrise, winds are expected
to shift more northwest, with gusts in the 20-25 kt range (not
as gusty as today).

Otherwise, VFR conditions are expected through the period, cloud
bases generally 6-8 kft or higher.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 7 PM CDT this evening for Winthrop
     Harbor IL to Gary IN.

&&

$$

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